As described by Shigeyasu Kobayashi, "Interferon", published by Kodansha Co. Ltd., Tokyo, Japan (1975), D. A. J. Tyrrell, "Interferon and Its Clinical Potential", published by William Heineman Medical Books Ltd. (London) (1976), and in "Protein, Nucleic Acid and Enzyme", vol. 21, no. 4 (1976), interferon is the term designated for a proteinaceous substance which is intra- or extra-cellularly induced by exposing living cells to the action of an interferon inducer, for example virus, bacterium, protozoon, rickettsia, nucleic acid, endotoxin and polysaccharide, and which has a function to inhibit non-specifically the multiplicaton of various virus in cells. Because of its viral multiplication inhibitory function, interferon has been long considered as a promising therapeutic and prophylactic agent for viral diseases since its discovery. Recently, it has been demonstrated that interferon acts as an anti-tumor agent not only on viral tumor but also on non-viral tumor, and therefore, the realization of interferon as a medicine has been in great expectation.
It is well documented that the term interferon involves Type I and Type II interferons; the former, Type I interferon or classical interferon with a molecular weight of about 1-3.times.10.sup.4, which is induced by exposing living cells to viral infections, and the latter, Type II interferon or immune interferon with a molecular weight of about 4-7.times.10.sup.4, which is induced in lymphocytes on stimulation with mitogens or on response to antigens. As described by L. B. Epstein, "Texas Reports on Biology and Medicine", vol. 35, pp. 41-56 (1977), published at the University of Texas Medical Branch, Galveston, Tex., U.S.A., Type II interferon is less stable than Type I interferon under vigorous conditions; at a pH below 2 and above 10, and/or at a temperature above 56.degree. C. Since Type II interferon, however, has a close relationship to immunoreactions, Type II interferon is expected to have much higher therapeutic and prophylactic efficacies on interferon-sensitive diseases than Type I interferon.
Due to its high species-specificity, the therapeutic and prophylactic efficacies on human diseases are not realizable with interferon which is obtained from other sources than living human cells. So far leukocytes are used in the preparation of Type II interferon. An attainment of a large amount of Type II interferon at a low cost from leukocytes is quite difficult because leukocytes must be separated and prepared from fresh blood, and do not bear long-period storages. Due to the circumstances, commercial production of Type II interferon feasible as a therapeutic and prophylactic agent for human diseases has not been realized.